neurons, learning, and dopamine

HOW NEURONS LEARNNeuroscience – 10/9/2013

What is learning?

Take a few moments and produce your own definition of what learning is.

Consider—What kinds of things do you learn?How do you learn them?

Different Domains of LearningCOGNITIVE

Facts and information Procedures (how to

solve a problem)

PSYCHOMOTOR Physical patterns of

activity

AFFECTIVE Learning to “feel”

something

Write your own example of: Cognitive Learning

Psychomotor Learning

Affective Learning

What do these types of learning have in common?

My brain, pre learning: STIMULUS 1 RESPONSE 1(Shakespearean sonnet) (ennui)

My brain, post learning:STIMULUS 1 RESPONSE 2!!!!!(Shakespearean sonnet) (happiness!)

Learning is the association of stimuli with new responses.

How does learning occur?

Our brain has about a hundred billion neurons, but we do not grow new ones (mostly)

Instead , learning happens at the connection point between different neurons—at the synapse.

How can neurons change?

Growing longer dendrites/axons to make new synapses

Releasing more vesicles of neurotransmitter (presynaptic cell)

More receptors for neurotransmitter (postsynaptic cell)

In this picture, there are 3 things happening to strengthen this synapse. Can you find them?

Dopamine

Dopamine is a particular neurotransmitter with many roles in the brain, including: - Cardiovascular and renal control- Movement and balance- Reward and addiction- Pleasure, emotion- Normal cognitive function (thinking)

Dopamine and disease

Dopamine deficiency in certain parts of the brain is related to Parkinson’s and motion disorder.

Excessive dopamine has been linked to schizophrenia and delusions.

Mechanisms of Drug Action

A dopamine agonist would bind to receptors instead of dopamine and convince your neurons that dopamine was there.

A dopamine antagonist would bind to receptors instead of dopamine and block normal activation.

Other drugs inhibit reuptake, leaving more dopamine in the synapse longer. (cocaine)

Indirect drugs cause extra dopamine release from all neurons (amphetamine)

Neurotransmitters convey “messages” across the synapse

Dopamine and Reward

Dopamine is involved in a brain circuit often called the “reward pathway”

In studies, we observe dopamine release when subjects are rewarded with food/money/etc

Generally, more dopamine is released when the reward is unpredicted

Dopamine/Opioids: Brain’s incentive reward systems

Activation of reward center produces a “wanting” and “liking” response

Natural events activate these reward systems

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Di Chiara et al., Neuroscience, 1999.

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Fiorino and Phillips, J. Neuroscience, 1997.

Natural Events Elevate Dopamine Levels

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Some drugs activate your reward systems since they act on the same receptors

Drugs make your brain really happy…..

Normal Brain Brain on Drugs

BUT only when your brain is on drugs.

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Effects of Drugs on Dopamine Release

Repeated use of drugs trigger compensatory processes and saturate the brain’s reward systems

individual can become conditioned/habituated/adapted to the intense level of drug-induced pleasure

the normal level of natural rewards are no longer experienced as very pleasurable

this is caused by synaptic changes—just like learning!

Upregulation

Downregulation

Too much dopamine activation at the synapses leads your neurons to decrease the number of receptors.

Brain on drugs after tolerance

Brain on drugs for an extended

period

Chronic drug taking ….reorganizes the liking and wanting systems

… drugs may no longer be pleasurable but you still want them…

Drugs can change your brain so that natural events are no longer pleasurable

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High DA receptor

Low DA receptor

DA Receptors and the Response to Methylphenidate (MP)

As a group, subjects with low receptor levels found MP pleasant while those with high levels found MP unpleasant

Adapted from Volkow et al., Am. J. Psychiatry, 1999.

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